Liquid flow detecting device

DETAILED DESCRIPTION What is claimed is: 1.
A liquid flow detecting device incorporating a static member arranged to be fixed within a passage through which flow of an operating liquid is to take place and an active member held captive in space by the static member but physically separate from the static member and free to undergo a displacement relatively to the static member to a limited extent in one particular direction at least and having an overall specific gravity substantially the same as that of the chosen operating liquid and proximity sensing apparatus operative to detect movement of the active member relative to the static member in the particular direction and issue a corresponding signal.
2.
A device as claimed in claim 1 in which the static member comprises a part of generally cylindrical shape and a post attachable to a fixed support to which the static member is attached in a crosswise position, the active member comprises a hollow cylindrical shell enclosing the inner static member and being a loose sliding fit therein, the post projecting through an aperture in the side wall of the hollow cylindrical member and the proximity sensing apparatus incorporates at least one pair of co-operating elements one of which is attached to the inner static member and the other of which is attached to the outer active member.
3.
A device as claimed in claim 2 in which one element of the pair is attached to one end of the static member and the other element is attached to the adjacent end of the active member.
4.
A device as claimed in claim 2 in which the proximity sensing apparatus incorporates two independent pairs of elements located at opposite ends of the active and passive elements.
5.
A device as claimed in claim 2 in which the inner static member is formed of two cylindrical portions attached to the post concentrically on opposite sides of the post so that the upper end of the post becomes in effect a part of the static member.
6.
A device as claimed in claim 2 in which a flexible tubular casing surrounds the post and is arranged to be sealed at one end to the support and is sealed at the other end to the active member to surround and enclose the aperture in the side wall of the hollow cylindrical shell of the active member